Nanoparticles/nanostructures

The above sections should clearly demonstrate that the study of graphene and its hybrids, especially the latter, has only just begun. Hybrids of graphene with various inorganic nanostructures (nanoparticles, nanowires and nanosheets) are likely to possess many novel properties with potential applications. Graphene-MOF hybrids are yet to be explored extensively and they are found to reveal many useful properties. 

Poudel, P. Qiao, Q., One dimensional nanostructure/nanoparticle composites as photoanodes for dye-sensitized solar cells. Nanoscale 2012,4 2826-2838. 

In a particular case of copper nanostructures, nanoparticles have the form of metallic nuclei of radius R — 1.7 nm coated with a Cu20 sheath of thickness d — 0.7 nm with ed as 4 [38]. For structures of this kind, the dependence of the fraction of charged particles on the dielectric constant of the solution is presented in Figure 15.7. Substitution of these values in expression (5) gives A/A0 10- This value is in reasonable agreement with the experimental data presented below. 

For a material that consists of small particles, the specific surface area increases considerably with decreasing particle size. Similarly, nanoporous materials exhibit high surface areas. Compare the two types of nanostructures (nanoparticles and nanopores) and describe why both lead to high values of specific surface area. 

The geometric and surface properties of supported nanostructures (nanoparticles, nanorods, and other nanoscale objects) are closely related to many of their important applications. On relatively inert substrates, such as graphite, oxides, and nitrides, many nanostmctures can be fabricated in a nearly free-standing state by simple physical vapor deposition, and be characterized using electron microscopy, scanning probe microscopy, and various spectroscopic methods. Their intrinsic properties, including the interaction among them, can be measured. In addition, the nanostructures on an inert support provide us with an arena to examine their interactions with other nanoobjects, such as biomolecules, without the influence of a solution. 

The engineering of novel deviees requires, in many eases, materials with finely seleeted and preestablished properties. In partieular, one of the most promising lines of synthetic materials research consists in the development of nanostructured systems (nanocomposites). This term describes materials with structures on typical length scale of 1-100 nm. Nanometric pieces of materials are in an intermediate position between the atom and the solid, displaying electronic, chemical and structural properties that are distinct from the bulk. The use of nanoparticles as a material component widens enormously the available attributes that can be realised in practice, which otherwise would be limited to bulk solid properties. 

A Ulman. An Introduction to Ultrathin Organic Films From Langmuir-Blodgett to Self-Assembly. Boston, Academic Press, 1991 JH Fendler. Nanoparticles and Nanostructured Films Preparation, Characterization and Application. Weinheim, Germany Wiley VCH, 1998. 

Considering that nanoparticles have much higher specific surface areas, in their assembled forms there are large areas of interfaces. One needs to know in detail not only the structures of these interfaces, but also their local chemistries and the effects of segregation and interaction between MBBs and their surroundings. The knowledge of ways to control nanostructure sizes, size distributions, compositions, and assemblies are important aspects of bottom-up nanotechnology [97]. 

The last problem of this series concerns femtosecond laser ablation from gold nanoparticles [87]. In this process, solid material transforms into a volatile phase initiated by rapid deposition of energy. This ablation is nonthermal in nature. Material ejection is induced by the enhancement of the electric field close to the curved nanoparticle surface. This ablation is achievable for laser excitation powers far below the onset of general catastrophic material deterioration, such as plasma formation or laser-induced explosive boiling. Anisotropy in the ablation pattern was observed. It coincides with a reduction of the surface barrier from water vaporization and particle melting. This effect limits any high-power manipulation of nanostructured surfaces such as surface-enhanced Raman measurements or plasmonics with femtosecond pulses. 

Figure 10. Four different ways of controlling the kinetics of polyol reduction and the corresponding morphologies observed for the Pt nanostructures. As the same amount of PVP was present in all four syntheses illustrated here, the striking differences in morphology were not caused by variation in the PVP concentration. It is assumed that the PVP molecules in these syntheses function only as a stabilizer to prevent the resultant nanoparticles from aggregating into larger structures. (Reprinted from Ref [270], 2005, with permission from Wiley-VCH.)...

---